This invention relates to caster wheels, and, in particular, to a design for a caster wheel assembly which will prevent shimmying when operating a vehicle at relatively high speeds.
Caster wheels are commonly used on vehicles which operate at low speeds (10-15 m.p.h.). However, when the speed of the vehicle reaches 20 miles per hour, there is a problem of shimmying, which is an uncontrolled vibration or rotation of the caster kingpin about its axis. Various methods have been used in the past to reduce the problem of shimmying. Some designs have used hydraulic fluids and flow resisting devices in order to restrain movement of the caster wheel regardless of the speed of the vehicle. Some of these hydraulic dampers operate only at certain positions of the caster wheel and others operate for the entire 360.degree. of rotation of the kingpin.
In the case of casters used for airplane landing wheels, it is known to provide a continuous friction force at all times (for the limited angles of operation of the caster wheel), and, upon contact of the caster wheel with the ground during landing, to mechanically lock the caster kingpin in the position which it assumes upon landing. These airplane landing wheels are not typical caster wheels, because the axis of the wheel and the axis of the caster kingpin are coplanar while, in a typical caster, the axis of the wheel always lies behind or follows the axis of the kingpin. This design means that the airplane landing wheels are not required to rotate 180.degree. when the airplane reverses direction (unlike the typical caster wheel design). The locking of the caster kingpin prevents rotation of the kingpin entirely and would not be suitable for applications in which it is necessary to change the direction of the vehicle during operation. The limited angles of operation also would not be suitable for applications in which the caster must reverse direction, where the kingpin must be capable of rotating 360.degree. about its axis. The constant friction which is used in many arrangements is also not desirable, because it makes maneuvering of the vehicle relatively difficult at low speeds, when there is no problem with shimmying.